Macrocyclic ketones, e.g., civetone represented by the following general formula (1), are known as fragrant ingredients of musk, and are sold at very high prices. 
A large number of reports have been made on the processes for producing civetone (a recent review: Alvin S. Williams, Synthesis, 1999, 10, 1707-1723). For example, known is a process of using a diester of 9-octadecenedioic acid produced by metathesis of an ester of oleic acid as an starting material, forming an α-alkoxycarbonylated macrocyclic ketone by Dieckmann condensation and an α-carboxy macrocyclic ketone by hydrolysis, and then subjecting the α-carboxy macrocyclic ketone to decarboxylation (Choo, Yuen et al., J. Am. Oil Chem. Soc. 1994, 71(8), 911-913).
By the way, in so-called Claisen condensation wherein esters having α-hydrogen are condensed in the presence of a strong base to form a β-ketoester, Dieckmann condensation used in the above process is particularly called by that name when two esters involved in the reaction are present in the same molecule and an α-alkoxycarbonylated macrocyclic ketone is formed. In general, Dieckmann condensation is advantageous to the formation of 5-, 6-, or 7-membered ring.
In the case of forming a 13-membered or larger ring by Dieckmann condensation, because the probability of an intermolecular reaction of esters becomes higher than that of an intramolecular reaction of esters when the esters are reacted at a usual concentration, the ring closure is carried out according to a high dilution process (Advanced Organic Chemistry, 4th ed., Jerry March, John Wiley & Sons, 1992, 491-493).
Accordingly, also in the above synthesis of civetone, the synthesis is carried out under a highly diluted condition of a concentration of 0.024 mol/L using a strong base of potassium hydride as a Dieckmann condensation reagent, and thus the reaction efficiency is very bad.
Recently, the present inventors have reported a novel process for Claisen condensation (Dieckmann condensation) using titanium tetrachloride (TiCl4), tributylamine (Bu3N) and, if necessary, chlorotrimethylsilane (TMSCl) catalyst (Y. Tanabe et al., Tetrahedron Letters 1999, 40, 4227-4230). According to the process, α-carbomethoxycyclopentanone having a 5-membered ring can be obtained in 95% yield by reacting dimethyl ester of hexanedioic acid in dichloromethane at −78° C. for 2 hours in the presence of TiCl4, Bu3N, and TMSCl catalyst.
As a result of the intensive studies on the process for Dieckmann condensation newly found, the inventors have found that, also in the ring formation of a diester of a long-chain dicarboxylic acid having 18 or more carbon atoms, surprisingly, an intramolecular reaction of esters proceeds predominantly over an intermolecular reaction of esters even when the reaction is carried out not according to a high dilution process but at a usual concentration.
The invention aims at solving the above problem, and an object of the invention is to provide a process for producing a macrocyclic ketone efficiently, which permits high concentration synthesis.